In TDM digital transmission systems, synchronization and clock recovery are facilitated by some form of correlation on a synchronization word. If the received synchronization word is corrupted in any way (e.g., Rayleigh fading), clock recovery may be sub-optimal, and the resulting bit-error rate (BER) subsequently degraded. For a background on Rayleigh fading, reference is made to George Calhoun, DIGITAL CELLULAR RADIO, published in 1988 in the United States of America. For the case when the synchronization word is severely corrupted (e.g., a fading null occurs in the middle of the synchronization word), the entire data within that timeslot may be lost. In a diversity receiver, the recovered clock in one branch can be corrupted to cause a degraded overall received signal in the diversity combining algorithm. In digital cellular systems, these problems make it difficult to achieve a 10.sup.31 6 BER at high signal levels in Rayleigh faded environment.
The difficulty to achieve 10.sup.31 6 BER at high signal levels makes it difficult to choose data detectors to be used within the diversity receiver. For example, a maximum ratio (max-ratio) diversity coherent detector offers performance improvements over a single branch coherent detector, especially at low signal levels. For strong RF signals however (i.e., greater than -95 dBm), the max-ratio detector exhibits a BER "floor" of 1.times.10.sup.31 5 in a Rayleigh faded environment. The 10.sup.31 6 can be met using a selection diversity delay detector, but performance at low RF signal levels is compromised. For BER between 2.times.10.sup.31 4 and 2.times.10.sup.31 5 (for radio with a noise Figure of 8 dB, this approximately corresponds to RF signal levels between -92 dBm and -98 dBm), the max-ratio coherent detector and the selection diversity delay detector yield similar results. Conventional detector selection methods based on received signal strength indication (RSSI) could be used, but would require having a balanced RSSI measurement between the two diversity branches which is difficult to achieve in the receiver design. Use of a detector eliminates the need for the use of signal strength from the radio which in turn makes the radio insensitive to errors in RF signal level measurements. If only RF signal strength measurements were used, a small error in RF signal level would result in a significant BER degradation due to the significant relationship between the BER and the RF signal level.
Thus, a need exists for a diversity receiver which employs improved clock recovery and/or detector selection algorithm for use in data recovery which meets, inter alia, demanding receiver performance specifications.